I'm sure this will be different for each vehicle. Driving '07 Tahoe with 5.3 and 3.73 ratio and heavy duty towing package. I'm wondering what transmission temperature would be considered OK or not OK while towing. Normal interstate driving no trailer, 70mph degrees air temp at 70mph I seem to stay at about 175-180 degrees on transmission. Towing 4400 trailer at 60mph temp was running just over 200. I'm supposed to have a trans cooler (although I can't phsycally see it as I could on Expdition) but have no idea what 'normal' would be while towing.
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200 would be about normal if you were climbing a grade on a warm day. Not apt to be dangerous to your transmission as long as it doesn't get a LOT hotter when you're actually working it. Working it hard on very hot days would usually get you somewhere around 220 or so. Your normal transmission temp will very depending on the ambient temperature where you're driving also.
Good luck / Skip
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I agree that the transmission fluid is at the upper limit of deciding to do something or not. Sort of a gray area, if it was 220, I would say install a second cooler - one you can see, not just the transmission fluid to engine coolant cooler in the water tank. At 180, I consider that on the low side of normal, I would actually need to see it about 175 on each winter driving trip to consider that water will not condense in the transmission fluid, so it is ideal.
I would try towing something heavier - if you plan on towing something heavier in warmer weather to check and see if 200 is your "Normal" for that size trailer and it will only get warmer, of if the factory cooler will kick in better in warmer weather and stay at 200 all the time, even with a heavier trailer.
My thought is get a secondary cooler, and install it on the transmission cooler return line, and then you will have little to worry about. Yet because it is so close to the "Gray area" not doing anything will not provide bad results, until you tow something that is much heavier in 95F weather and the transmission starts to go above 220F. If you reach 230F, then the idea is to slow a bit to allow the engine to cool, and this will reduce the load on the transmission, cooling everything off. So if you are patient on he mountain grades, then you probably will not need the transmission cooler.
You can still tow up a grade with 235F peak transmission temperatures and it will not quickly degrade, however that is a very warm temperature for the transmission to be running at, and you should consider flushing the transmission after returning home. If you reach 250, slow way down, if it does not drop below 235 right away, consider your options to pull off the roadway into a wide area, and see if the transmission has a problem, or if the coolant line is leaking or broken. Yet with a hot engine, don't shut it off right away (this stops the cooling pump and fan) unless you have bigger problems such as leaking water or fluids.
Remember that it is increased horsepower that overloads the radiator and transmission cooler, so going up the mountains slower requires less horsepower, thus the engine is much less likely to overheat.
Seems a little high for the conditions you listed, I'd install a aux cooler.
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200 is no problem towing. Like above 220 is getting too much. If the trans has never been serviced, you should do that. It would be a good idea to have synthtic fluid put in. It will tolerate more heat without breaking down.
I think it's normal, and I wouldn't worry about adding additional cooling.
I don't mean to sound like a smart guy, but have you checked the owners manual? maybe they mention a "range" in there. I have recently added a digital trans temp gauge to my truck, but haven't towed with it installed yet, thanks to my location here in the Great White North . My truck runs about 180-185 non towing.
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edited 02/17/12 08:40pm by an administrator/moderator *
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